Method and apparatus for parallel desalting

Abstract

Parallel desalting (PDS) includes a hybrid membrane softening (MS) system for de-mineralizing water for residential and commercial use. Parallel desalting produces “soft” water without the use of salt, or any other liquid chemical reagent normally used to carry out pH adjustment in industrial membrane and precipitation processes. The PDS process balances the operation of a RO (potable water) membrane unit with the operation of a tubular MF (wastewater) membrane unit, thereby providing a highly efficient and regenerative water treatment technology: (1) The optimum operation for the PDS system transforms roughly 90 percent of a potable, slightly brackish water supply into <50 mg/L TDS water with <1-grain (10–15 mg/L as calcium carbonate)—water hardness; and (2) The operation of the PDS system produces, in salinity terms, in a 100 percent reusable effluent for downstream recycling. Virtual prototype results suggest that with Colorado River Aqueduct source water (570–620 mg/L TDS and 16-grain water hardness), parallel desalting can produce an effluent with a TDS 40–70 mg/L lower than the originating supply (excluding TDS contributed directly by the particular type of use of the soft water).

1. Apparatus for membrane softening of potable water, said apparatus comprising:
 a reverse osmosis (RO) membrane for softening and demineralizing potable water, said reverse osmosis (RO) membrane producing an (RO) permeate and an (RO) concentrate; 
 a microfiltration (MF) membrane for receiving the (RO) concentrate and producing an (MF) permeate and (MF) concentrate; 
 hydraulic pathways for recycling the (MF) permeate to the potable water for return to said reverse osmosis (RO) membrane at a pH level suitable for suppressing deposition of solids on the reverse osmosis (RO) membrane; 
 a pressurized concentrate storage tank including seed crystals, the storage tank being in fluid communication between the reverse osmosis (RO) membrane and the microfiltration (MF) membrane for receiving (RO) concentrate at a pH that is conducive to metastable precipitation of calcium carbonate on the seed crystals; and 
 lines for delivery of (RO) permeate for use. 
 
     
     
       2. The apparatus according to  claim 1  wherein said hydraulic pathways comprise a permeate storage tank interconnected between the (RO) membrane and the delivery lines. 
     
     
       3. The apparatus according to  claim 2  further comprising a permeate delivery pump for both providing water pressure to the delivery lines and for recirculation of (RO) permeate through the (RO) membrane for cleaning thereof, a recirculation line for enabling the recirculation of (RO) permeate through the (RO) membrane and a control system for causing the permeate delivery pump to operate so as to either provide water pressure to the delivery lines or to recirculate (RO) permeate through the (RO) membrane. 
     
     
       4. The apparatus according to  claim 3  further comprising a circulation pump for recycling the portion of (RO) concentrate to the potable water and for recirculation of stored concentrate from said concentrate storage tank through the (MF) membrane, a line interconnecting the (MF) membrane and said concentrate storage tank enabling the recirculation of the stored concentrate from said concentrate storage tank and said control system is operable for causing the circulate pump to operate so as to recycle portion of the (RO) concentrate to the potable water and to recirculate stored concentrate from the concentrate storage tank through the (MF) membrane. 
     
     
       5. The apparatus according to  claim 4  wherein said hydraulic pathways comprise a line interconnecting said concentrate storage tank and a drain for disposal of concentrate storage tank contents. 
     
     
       6. Apparatus for membrane softening of potable water, said apparatus comprising:
 a reverse osmosis (RO) membrane for non-chemical softening and demineralizing potable water, said reverse osmosis (RO) membrane producing an (RO) permeate and an (RO) concentrate; 
 a microfiltration (MF) membrane for receiving the (RO) concentrate and producing an (MF) permeate and (MF) concentrate without chemical addition; 
 hydraulic pathways for recycling the (MF) permeate to the potable water for return to said reverse osmosis (RO) membrane without addition of any chemical and at a pH level suitable for suppressing deposition of solids on the reverse osmosis (RO) membrane; 
 a pressurized concentrate storage tank including disposed seed crystals, the storage tank being in fluid communication between the reverse osmosis (RO) membrane and the microfiltration (MF) membrane for receiving (RO) concentrate at a pH that is conducive to metastable precipitation of the calcium carbonate on the seed crystals; and 
 lines for delivery of (RO) permeate for use. 
 
     
     
       7. The apparatus according to  claim 6  wherein said hydraulic pathways comprise a permeate storage tank interconnected between the (RO) membrane and the delivery lines. 
     
     
       8. The apparatus according to  claim 7  further comprising a permeate delivery pump for both providing water pressure to the delivery lines and for recirculation of (RO) permeate through the (RO) membrane for cleaning thereof, a recirculation line for enabling the recirculation of (RO) permeate through the (RO) membrane and a control system for causing the permeate delivery pump to operate so as to either provide water pressure to the delivery lines or to recirculate (RO) permeate through the (RO) membrane. 
     
     
       9. The apparatus according to  claim 8  further comprising a circulation pump for recycling the portion of (RO) concentrate to the potable water and for recirculation of stored concentrate from said concentrate storage tank through the (MF) membrane, a line interconnecting the (MF) membrane and said concentrate storage tank enabling the recirculation of the stored concentrate from said concentrate storage tank and said control system is operable for causing the circulate pump to operate so as to recycle the portion of the (RO) concentrate to the potable water and to recirculate stored concentrate from the concentrate storage tank through the (MF) membrane. 
     
     
       10. The apparatus according to  claim 9  wherein said hydraulic pathways comprise a line interconnecting said concentrate storage tank and a drain for disposal of concentrate storage tank contents. 
     
     
       11. A method for softening and demineralizing of potable water, said method comprising the steps of:
 providing a reverse osmosis (RO) membrane; 
 introducing potable water to said reverse osmosis (RO) membrane in order to produce an (RO) permeate and an (RO) concentrate; 
 providing a microfiltration (MF) membrane; 
 introducing the (RO) concentrate to said microfiltration (MF) membrane to produce an (MF) permeate and an (MF) concentrate; 
 recycling the (RO) permeate to the potable water for return to said reverse osmosis (RO) membrane; 
 recycling a portion of the (MF) concentrate to the potable water for return to said reverse osmosis (RO) membrane at a pH level suitable for suppressing deposition of solids on the reverse osmosis (RO) membrane; 
 providing a pressured concentrate storage tank including seed crystals; 
 introducing the (RO) concentrate into said concentrate storage tank at a pH that is conducive to metastable precipitation of calcium carbonate on the seed crystals; and 
 providing (RO) permeate for use through a delivery line.